Studies on phosphate-solubilizing bacteria in soil and rhizosphere of different plants. II. Selection of the most efficient phosphate-dissolvers and their morphological grouping.

Two hundred colonies which showed positive reaction on the plates prepared for the phosphate-dissolving bacteria from control soil rhizosphere soils and rhizoplane samples of maize, peas, or cotton were isolated at random. Fifty isolates were selected as the most efficient isolates according to their capability for increasing the amounts of available phosphorus in the media with corresponding decreases in pH values. The percentage of the most efficient isolates differed according to type of plant and location of isolation. Not only the morphological types of the phosphate-dissolving bacteria differed in soil and in rhizosphere, but they also differed in the rhizosphere soil of each special plant. Morphological differences in the isolates from rhizosphere soil and from rhizoplane samples of the same plant were also occurring. The abundance of mycelial-forming bacteria and of aerobic sporeformers in Egyptian soil is important as they are well known to resist adverse conditions, such as high temperature and dryness to which our soils are subjected most time of the year.